290 BOTANICAL GAZETTE [OCTOBER 
7. In the cocklebur the bur aids in preserving the seed coat of 
the upper seed by being most persistent over it. 
8. Even in the hawthorns, where the delay is secured by embryo 
characters, the germination finally comes about in the course of 
long exposure to germinative conditions and not in dry storage. 
g. In the cocklebur the seed coats of both the upper and lower 
seeds cut down the oxygen supply, but the first the more markedly. 
This gives the upper seed a much higher minimum germinative 
temperature and the lower seed a somewhat higher one. Hence we 
have in the cocklebur seeds two minimum germinative temperatures; 
one with the seed coats intact and a much lower one with the coats 
removed. In the‘upper seeds these differ by fifteen or more degrees; 
in the lower seeds by three to five degrees. 
to. High temperatures bring about the germination of the upper 
seeds of the cocklebur with coats intact by increasing the rate of 
diffusion of oxygen through the seed coat and by raising the respira- 
tory ratio. 
11. The minimum germinative temperatures of the seeds of the 
cocklebur, Plantago major, P. Rugelii, Thlaspi arvense, and various 
other seeds, with the seed coats intact, is far above the highest mini- 
mum germinative temperature repuried: while in the cocklebur and 
Plantago major with coats removed this critical temperature is 
considerably above the highest reported. 
I am indebted to Professor Cuas. F. Horres, of the University of 
Illinois, for suggesting the problem in reference to the cocklebur, and 
to Professors Joun M. Coutrer and C. R. Barnes for kind suggestions 
and assistance during the progress of the work. 
ray LITERATURE CITED. 
1. ARTHUR, me C., Delayed germination in the cocklebur and other paired 
roc. Soc. Prom. Agric. Science 16:70-79. 1895. 
2. Derurs, itp , Keimungsprocess der Samen 427. 1880 
3a. Duvet, J. W. T., Vitality and ere of exile. U. S. Dept. Agric. 
Bur. Plant Ind., Bull. 58. 
eae. , Vitality of buried an ties: Bull. 83. 1905. 
4. Kienrrz, M., Ueber Ausfiihrung von Keimproben. Bot. Centralbl. 1752753 
1880. 
